Monoflange valves are typically used for pressure instrumentation take-off points, isolation, sampling, injection, venting, or purging of processing fluids. These monoflange valves typically have a valve body with a flange interface for mounting directly onto a flanged connection located upstream or downstream of processing equipment. Known monoflange valves typically have an axial inlet passage and an outlet passage for communicating the processing fluid from a main fluid conduit to a pressure gauge or other instrumentation. In addition, known monoflange valves typically include two or more valve assemblies and corresponding valve seats disposed within the valve body between the inlet passage and outlet passage for blocking fluid flow and isolating such instrumentation, or for venting fluid from the valve body.
Providing multiple valve assemblies within the same monoflange valve body enables a relatively compact design, and therefore such monoflange valves are typically used as an alternative to multi-valve systems that require separate flange adapters. The more compact monoflange valve design also reduces the number of potential fluid leakage paths compared to multi-valve designs, which is useful when such monoflange valves are used in severe service media applications. When used in severe service applications, the valve assemblies disposed within the monoflange valve body are often sealingly attached to the monoflange valve body via welding for preventing the severe service media from leaking out of the valve body. To ensure zero defect and leakage from the welds, the welding interfaces may require 100% weld penetration and 100% radiographic inspection.